Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, a person may have hearing loss of both types. Of them, conductive hearing loss occurs where the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss may often be helped by use of conventional hearing aids, which amplify sound so that acoustic information does reach the cochlea and the hair cells.
In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. This type of hearing loss is due to the absence of, or destruction of, the hair cells in the cochlea which transduce acoustic signals into nerve impulses. These people are thus unable to derive suitable benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is made, because there is damage to or absence of the mechanism for nerve impulses to be generated from sound in the normal manner.
It is for this purpose that cochlear implant systems have been developed. Such systems bypass the hair cells in the cochlea and directly deliver electrical stimulation to the auditory nerve fibres, thereby allowing the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered to the auditory nerve. U.S. Pat. No. 4,532,930, the contents of which are incorporated herein by reference, provides a description of one type of traditional cochlear implant system.
Typically, cochlear implant systems have consisted of essentially two components, an external component commonly referred to as a processor unit and an internal implanted component commonly referred to as a receiver/stimulator unit. Traditionally, both of these components have cooperated together to provide the sound sensation to a user.
The external component has traditionally consisted of a microphone for detecting sounds, such as speech and environmental sounds, a speech processor that converts speech into a coded signal, a power source such as a battery, and an external transmitter coil.
The coded signal output by the sound processor is transmitted transcutaneously to the implanted receiver/stimulator unit situated within a recess of the temporal bone of the user. This transcutaneous transmission occurs via the external transmitter coil which is positioned to communicate with an implanted receiver coil provided with the stimulator/receiver unit. This communication serves two essential purposes, firstly to transcutaneously transmit the coded sound signal and secondly to provide power to the implanted receiver/stimulator unit. Conventionally, this link has been in the form of a radio frequency (RF) link, but other such links have been proposed and implemented with varying degrees of success.
The implanted receiver/stimulator unit traditionally includes a receiver coil that receives the coded signal and power from the external processor component, and a stimulator that processes the coded signal and outputs a stimulation signal to an intracochlea electrode assembly which applies the electrical stimulation directly to the auditory nerve producing a hearing sensation corresponding to the original detected sound.
Traditionally, at least the speech processor of the external componentry has been carried on the body of the user, such as in a pocket of the user's clothing, a belt pouch or in a harness, while the microphone has been mounted on a clip mounted behind the ear or on the lapel of the user.
More recently, due in the main to improvements in technology, the physical dimensions of the sound processor have been able to be reduced allowing for the external componentry to be housed in a small unit capable of being worn behind the ear of the user. This unit allows the microphone, power unit and the sound processor to be housed in a single unit capable of being discretely worn behind the ear, with the external transmitter coil still positioned on the side of the user's head to allow for the transmission of the coded sound signal from the sound processor and power to the implanted stimulator unit.
It is further envisaged that with continual improvements in technology all the traditional external componentry may be implanted in the user. In such a system all of the speech processing may be performed inside the implanted stimulator unit, via an implanted microphone.
It is known in the art that the cochlea is tonotopically mapped. In other words, the cochlea can be partitioned into regions, with each region being responsive to signals in a particular frequency range. This property of the cochlea has been exploited by providing the electrode assembly with an array of electrodes, each electrode being arranged and constructed to deliver a stimulating signal within a preselected frequency range, to the appropriate region within the scala tympani of the cochlea. The electrical currents and electric fields from each electrode stimulate the nerves disposed on the modiolus of the cochlea.
Despite the enormous benefits offered by cochlear implants, one potential disadvantage of placement of the electrode assembly within the scala tympani is that it is necessary to breach the internal ducts of the cochlea, generally the scala tympani. The breaching of the scala tympani of the cochlea adversely affects the hydrodynamic behaviour of the cochlea and is thought to prevent or at least reduce any chance of preservation of any residual hearing of the implantee. This can be problematic for those persons who would benefit from use of a cochlear implant to improve hearing of relatively high frequencies but who have some residual hearing of relatively low frequencies. In such a case, the implantee is forced to trade off an existing residual capacity to hear relatively low frequency sounds against the desirability of being able to have a hearing sensation of relatively high frequency sounds offered by a cochlear implant.
There have been a number of proposals put forward to provide a hybrid system whereby a cochlear implant system can be used in conjunction with residual hearing, usually assisted by the use of a hearing aid. One such example of a proposed system is described in International Patent Application No WO 00/69512. In this application, the hybrid system utilises a hearing aid to amplify the low frequency sound enabling the user to rely on normal hearing processes to experience such sounds. For high frequency sounds, the hybrid system utilises a relatively conventional cochlear stimulation device consisting of a short cochlear electrode array. The short cochlear electrode array of this application is described as consisting of 4-8 electrodes and is inserted directly through the round window membrane making contact with the basal region of the cochlea. Therefore the system as described in this application still uses a relatively obtrusive electrode array making it very difficult to preserve any residual hearing the patient may have in such areas.
As already described, the present application is also directed to a device for masking or treating tinnitus. Tinnitus is the medical term for a condition in which sufferers report a ringing in their ears or head when there is in fact no external sound present in the sufferer's audible range. Although some people hear a ringing noise, others report the noise as being a hissing, a chirping, or a clicking. There are various estimates as to how many sufferers of tinnitus there are worldwide. For example, it is suggested that some 50 million Americans suffer from tinnitus, with about 83% of them hearing a constant ringing. Other figures suggest at least 12 million people have tinnitus to what is regarded as a distressing degree.
For some people, tinnitus is just a nuisance. For others, it can be a quite debilitating condition. Usually, the only relief tinnitus sufferers will experience is an occasional reduction in the loudness of the tinnitus from time to time.
The cause of tinnitus or at least its onset is unclear. There is, however, data available that demonstrates that exposure to loud noise is a trigger for the condition. Other suggested triggers include severe head trauma, certain medications, sinus and respiratory infections, ear infections, wax build-up and certain types of tumours.
There are, as yet, no cures for tinnitus but there are several treatments currently used to provide at least some relief. One treatment is the use of what are commonly referred to as tinnitus maskers. One example of a tinnitus masker is disclosed in PCT Patent Application WO 90/07251. Tinnitus maskers are essentially small battery operated devices which are worn like a hearing aid behind or in the ear, and cover (mask) the tinnitus psychoacoustically by artificial sounds which are emitted, for example, via a hearing aid speaker into the auditory canal and which reduce the disturbing tinnitus as far as possible below the threshold of perception. The artificial sounds are often narrowband noise (for example, third octave noise) which in its spectral position and its loudness level can be adjusted via a programming device to enable the maximum position adaptation to the individual tinnitus situation. This form of treatment is available in several forms and when properly administered, has been demonstrated to assist in somewhere between 58% and 65% of cases. Masking is simply the addition of an outside sound that serves as a substitute or mask for the tinnitus.
Masking systems known to date are typically worn within the ear canal or positioned nearby so as to ensure provision of a masking sound to the sufferer and as a result these devices stigmatise the wearer and are worn reluctantly.
Implantable tinnitus maskers are known, such as that described in U.S. Pat. No. 5,795,287. Such devices utilise electromechanical transducers coupled to the ossicular chain to produce the artificial masking sounds, however, these devices require a very complicated surgery to implant as the electromechanical transducer must mechanically manipulate the ossicular chain. Also, it has been found that such mechanical coupling is not always guaranteed to be stable as pressure necroses in the area of the middle ear ossicle has been found to occur in a number of cases resulting in bone erosion.
The present invention relates to a new system for treating the symptoms of tinnitus that preferably does not require complicated surgery nor the fixation of electromechanical transducers to the ossicles.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.